Certain drugs may have to be delivered in large doses, sometimes several times per day, to achieve a desired therapeutic effect. While large daily doses of drug may be administered by multiple dosing throughout the day, multiple dosing regimens are often not preferred because of patient compliance problems, potential side effects and the dangers of overdosing. Accordingly, there has been a movement to once-a-day or twice-a-day dosing regimens when possible, even when there is a need for large doses of drug to be delivered over a prolonged period, for example 12 hours to 24 hours, as the case may be.
High ranges of daily dosing may require drug loading in drug compositions of the dosage forms to be as much as 20% to 90% or more of the overall weight of the composition. Such loading requirements may present problems in formulating compositions and fabricating dosage forms that are suitable for oral administration and can be swallowed without undue difficulty. High drug loading may present even greater problems when formulating dosage forms that are to be administered a limited number of times per day, such as for once-a-day dosing, because of the large unit dosage form required.
Various devices and methods have been described having intended utility with respect to applications with high drug loading. For example, U.S. Pat. Nos. 4,892,778 and 4,940,465, which are incorporated herein by reference, describe dispensers for delivering a beneficial agent to an environment of use that include a semipermeable wall defining a compartment containing a layer of expandable material that pushes a drug layer out of the compartment formed by the wall. The exit orifice in the device is substantially the same diameter as the inner diameter of the compartment formed by the wall.
U.S. Pat. No. 4,915,949, which is incorporated herein by reference, describes a dispenser for delivering a beneficial agent to an environment of use that includes a semipermeable wall containing a layer of expandable material that pushes a drug layer out of the compartment formed by the wall. The drug layer contains discrete tiny pills dispersed in a carrier. The exit orifice in the device is substantially the same diameter as the inner diameter of the compartment formed by the wall.
U.S. Pat. No. 5,126,142, which is incorporated herein by reference, describes a device for delivering an ionophore to livestock that includes a semipermeable housing in which a composition containing the ionophore and a carrier and an expandable hydrophilic layer is located, along with an additional element that imparts sufficient density to the device to retain it in the rumen-reticular sac of a ruminant animal. The ionophore and carrier are present in a dry state during storage and the composition changes to a dispensable, fluid-like state when it is in contact with the fluid environment of use. A number of different exit arrangements are described, including a plurality of holes in the end of the device and a single exit of varying diameter to control the amount of drug released per unit time due to diffusion and osmotic pumping.
Other devices in which the drug composition is delivered as a slurry, suspension or solution from a small exit orifice by the action of an expandable layer are described in U.S. Pat. Nos. 5,660,861, 5,633,011; 5,190,765; 5,252,338; 5,620,705; 4,931,285; 5,006,346; 5,024,842; and 5,160,743. Typical devices include an expandable push layer and a drug layer surrounded by a semipermeable membrane. In certain instances, the drug layer is provided with a subcoat to protect the drug composition in those portions of the gastrointestinal tract having acidic pH, to delay release of the drug composition to the environment of use or to form an annealed coating in conjunction with the semipermeable membrane. However, such devices generally are not well suited as dosage forms for high drug loading due to size requirements necessary to accommodate large amounts of drug in a slurry, suspension or solution, and the need to have an oral dosage form conveniently sized so that it can be swallowed.
Another dosage form is disclosed in U.S. Pat. 5,536,507 that describes a three component pharmaceutical formulation that utilizes, inter alia, a pH sensitive polymer, optionally including an osmotic agent, that will swell in the higher pH regions of the lower portion of the small intestine and the large intestine to release drug in those environments. Additional components of the dosage form include a delayed release coating and an enteric coating to provide a dosage form that releases very little, if any, of the drug in the stomach, a relatively minimal amount in the small intestine and reportedly about 85% or more in the large intestine. Such a dosage form provides a widely varying time-release of drug after administration that may not begin for 1-3 hours until the dosage form has passed from the stomach and an additional 3 hours or more for the dosage form to pass into the large intestine.
U.S. Pat. 5,169,638 describes a buoyant controlled release pharmaceutical powder formulation to be filled into capsules that uses a pH dependent polymer formed from alginic acid and hydroxypropylmethyl cellulose to release pharmaceuticals at a controlled rate. It appears from the disclosure that the capsule formulation was intended to mimic the characteristics of a tableted formulation.
In the case of high drug loading, it is often preferable that a large orifice, from about 50%-100% of the inner diameter of the drug compartment, is provided in the dispensing device so that the drug layer can be dispensed in a non-fluid state. When exposed to the environment of use, drug is released from the drug layer by erosion and diffusion. A common problem associated with the release of drug from prior art dosage forms in which the drug layer is dispensed from the delivery device in a dry state is that a residual amount of drug often is left in the device and not released to the subject. Upwards of 20-30% of the drug loading of the composition may remain in the device without being released. In order to compensate for that deficiency, prior art methods have routinely provided for overloading of drug such that the required amount is delivered notwithstanding that a substantial amount remains unreleased in the delivery device. Loading an excess amount of drug further exacerbates the problems of dosage forms that are large and difficult to swallow. Also, the added cost may be significant for active agents having a high material or manufacturing cost. Consequently, there is a need for improved delivery devices having an expandable push layer and a drug layer suitable for use with high drug loading that release substantially all of the drug from the device to the environment of use.